Edit:
After some more testing I found that it does random search after all not linear.
I've tested it an it seem to work as advertised, at least in CPU mode.
My test includes searching for a prefix similar to the puzzle transaction's 2nd address:
1CUNEB with full prvKey range.
The result is: it's consistently finding the key 0x03 in mere split second since it searched from 01 onward, not random.
If it is random, it could take a while to find another key for an address starting with
1CUNEB since it could gone for the the middle or end part of the search space.
But since it's consistently finding
1CUNEBjYrCn2y1SdiUMohaKUi4wpP326Lb, I'd say that it's linear.
Also tried
19EEC5 multiple times and it's also consistent at finding
19EEC52krRUK1RkUAEZmQdjTyHT7Gp1TYT (
prvKey 0x47B069).
Lastly, I tried specifying the range and it also used the indicated
--keyspace.
Test command used:
./vanbitcrackens1.1 -t 3 --keyspace 1300000000000000:13FFFFFFFFFFFFFF -r 10 -o 1vanbitcreacken-output.txt -stop 1AVJKw
Result: Found
1AVJKwzs9AskraJLGHAZPiaZcrpDr1U6AB which is within that range.